This project deals with the problem of the detection, quantitation and operation of RNA tumor virus genes in cellular DNA. The frequency of proviral sequences related to avian leukoses, sarcoma and "endogenous" oncornaviruses will be measured in normal and neoplastic tissues in chickens by means of RNA-DNA hybridization reactions between the 60-70 S viral RNA genome and cellular DNA. A technique of competative hybridization will be developed as a method for studying sequence relatedness between the several types of avian oncornaviruses and for detecting RNA transcript of proviral genes in cells.